Heretofore, an electrostatic induction conversion device such as a power-generating unit or a microphone has been proposed wherein an electret having an electric charge injected to an insulating material, is used.
As the material for such an electret, it has been common to use a chain polymer such as polycarbonate, polypropylene or polytetrafluoroethylene. Further, recently, it has been proposed to use a polymer having a fluoroalicyclic structure in its main chain (e.g. Patent Document 1), or a cycloolefin polymer (e.g. Patent Documents 2 and 3), as the material for such an electret.    Patent Document 1: JP-A-2006-180450    Patent Document 2: JP-A-2002-505034    Patent Document 3: JP-A-8-41260